1. Field of the Invention
The present invention relates to a lubricant for metal forming and the method of use of the lubricant. In particular, the lubricant is especially useful in the manufacture of cans from black plate or tin-free steel.
2. Description of the Prior Art
Until fairly recently, it was usual practice in the can-making industry to make cans out of tin-plated sheet steel. By this process, the tin-plated sheet steel was rolled in cylindrical form, welded or soldered and enclosed by the placement of end plates (i.e., a top and a bottom) to form the complete can. Cans manufactured in this manner are generally referred to in the can-making industry as "three-piece cans" (the three pieces being the cylindrical body, the bottom and the top).
In order to improve upon the previous three-piece tin-plated sheet steel cans, the can-making industry has commenced manufacturing cans from aluminum. Aluminum cans may also be made in the three-piece fashion. More recently, however, the can-making industry developed technology which enabled the can body to be drawn and ironed in a manner which resulted in one end, i.e., the bottom, being an integral part of the can body. The use of this technology requires that a second piece, namely a top, be attached to the cylindrically formed, enclosed-bottom body in order to create the finished can product. Such cans are generally referred to in the can-making industry as "two-piece, drawn and ironed cans".
The two-piece, drawn and ironed cans may be made from materials such as tin-plated steel or aluminum. In the situation in which the can is made of aluminum, the metallurgical properties of aluminum are such that it can be drawn and ironed with a minimum of supplemental lubrication. In the case of two-piece, drawn and ironed cans made from tin-plated steel, one skilled in the art will recognize that the tin acts as a protective barrier for beverage, foodstuff or other material to be packaged in the container and also acts as a lubricant to facilitate the drawing and ironing of the can.
While the foregoing methods of manufacturing produce cans which are of a high quality, it has been determined that the cost of producing such cans may be decreased substantially if the cans are manufactured from steel which is free of tin. Such steel is referred to interchangeably by those in the industry as "black plate", or "tin free" steel (for the purpose of the instant invention, the former designation will be used, it being understood that "black plate" steel and "tin plate" steel are synonymous). However, the metallurgical properties of black plate steel are such that it is not possible to simply draw and iron a can body (i.e., the cylindrical body with an enclosed end) as has been the case with either aluminum or tin-plated steel. Indeed, the use of black plate steel in the metal forming operations required to produce a can are such that a lubricant coating must be applied to the black plate steel prior to the forming operation. In addition, because the lubricant is only needed during the drawing and ironing operations, the lubricant must be capable of being easily removed from the can prior to subsequent treatment and filling.